1. Field of the Invention
This invention relates to an electrically controlled polymer system that contracts and relaxes when acted upon by an electric current. This makes it appropriate for use as an artificial skeletal or cardiovascular muscle or to replace hydraulic, servomotors or stepper motors in robotics. In the case of disease or injury, the occasion arises when human muscles require replacement or repair. In the case of robotic devices, the size, weight and power requirements of current devices is thought to be a disadvantage.
2. Description of the Prior Art
It is know that certain hydrophilic ionic polymers contract or relax in response to changes in the environment in which they exist. W. Kuhn, et al, "Reversible Dilation and Contraction by Changing the State of Ionization of High Polymer Acid Networks", Nature, Vol. 165, No. 4196, pp 514-516, (1950) discussed their work with a three-dimensional polymer network made by reacting Polyacrylic Acid with Polyvinyl Alcohol in various ratios. The result of this reaction was a water insoluble, but swellable material. A material of this type, insoluble but swellable, is commonly referred to as a hydrogel. They showed that a hydrogel of this type contracted when the pH was lowered, the temperature was raised or the ionic strength was increased.
The behavior of gels of this type in an electric field was discussed by T. Tanaka et al., "Collapse of Gels in an Electric Field", Science, Vol. 218, pp 457-469, (1982) and in subsequent patents including U.S. Pat. No. 5,100,933.
In his patent Tanaka et al. discusses the contractile character of a hydrolyzed polyacrylamide gel immersed in an acetone/water solution. They discuss the contractile phenomenon as the water to acetone ratio is changed. They further state that when an electric current is passed through the gel, it contracts.
Adolf et al. (U.S. Pat. No. 5,250,167) and subsequently, Shahinpoor (U.S. Pat. No. 5,389,222), discuss a device which they refer to as an actuator that uses the phenomenon of the Tanaka patent. Again, a hydrogel material is immersed in an ionic solution. The material is mounted such that current is passed through the solution and into the gel. It is also mounted so that as the gel contracts, the force is transferred to a device outside the actuator.